U.S. patent application number 14/171933 was filed with the patent office on 2015-08-06 for lithium sulfur battery pulse charging method and pulse waveform.
This patent application is currently assigned to Nissan North America, Inc.. The applicant listed for this patent is Nissan North America, Inc.. Invention is credited to Peter Aurora, Gregory DiLeo, Taehee Han, Xiaoguang Hao, Ellazar Niangar, Kenzo Oshihara, Nagappan Ramaswamy, Rameshwar Yadav.
Application Number | 20150221990 14/171933 |
Document ID | / |
Family ID | 53755584 |
Filed Date | 2015-08-06 |
United States Patent
Application |
20150221990 |
Kind Code |
A1 |
Ramaswamy; Nagappan ; et
al. |
August 6, 2015 |
LITHIUM SULFUR BATTERY PULSE CHARGING METHOD AND PULSE WAVEFORM
Abstract
Provided are methods and apparatus for charging a lithium sulfur
(Li--S) battery. The Li--S battery has at least one unit cell
comprising a lithium-containing anode and a sulfur-containing
cathode with an electrolyte layer there between. One method
provides controlled application of voltage pulses at the beginning
of the charging process. An application period is initiated after a
discharge cycle of the Li--S battery is complete. During the
application period, voltage pulses are provided to the Li--S
battery. The voltage pulses are less than a constant current
charging voltage. Constant current charging is initiated after the
application period has elapsed.
Inventors: |
Ramaswamy; Nagappan;
(Farmington Hills, MI) ; Aurora; Peter; (Ann
Arbor, MI) ; DiLeo; Gregory; (Ann Arbor, MI) ;
Hao; Xiaoguang; (Ann Arbor, MI) ; Han; Taehee;
(Farmington Hills, MI) ; Yadav; Rameshwar;
(Farmington Hills, MI) ; Niangar; Ellazar;
(Farmington Hills, MI) ; Oshihara; Kenzo; (Novi,
MI) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Nissan North America, Inc. |
Franklin |
TN |
US |
|
|
Assignee: |
Nissan North America, Inc.
Franklin
TN
|
Family ID: |
53755584 |
Appl. No.: |
14/171933 |
Filed: |
February 4, 2014 |
Current U.S.
Class: |
205/673 ;
204/229.4 |
Current CPC
Class: |
H01M 10/44 20130101;
C25F 1/00 20130101; H02J 7/007 20130101; H01M 10/4242 20130101;
H01M 10/425 20130101; H02J 7/00711 20200101; H01M 10/446 20130101;
H01M 10/052 20130101; H02J 7/00 20130101; H01M 10/42 20130101; H01M
2220/20 20130101; H02J 7/0069 20200101; H01M 10/46 20130101 |
International
Class: |
H01M 10/44 20060101
H01M010/44 |
Claims
1. A method of charging a lithium-sulfur battery having at least
one unit cell comprising a lithium-containing anode and a
sulfur-containing cathode with an electrolyte layer there between,
the method comprising: applying voltage pulses during an
application period, the application period initiated when a battery
charge cycle is initiated, wherein the voltage pulses are less than
a constant current charging voltage; and initiating constant
current charging after the application period has elapsed.
2. The method of claim 1, wherein application of the voltage pulses
is configured to create surface defects on lithium sulfide
particles.
3. The method of claim 1, wherein application of the voltage pulses
is configured to optimize coulombic efficiency of the battery.
4. The method of claim 1, wherein applying the voltage pulses
includes controlling pulse characteristics of each voltage pulse
during the application period.
5. The method of claim 4, wherein controlling pulse characteristics
comprises gradually increasing, in succession, a peak voltage of
each of the voltage pulses, each peak voltage being less than the
constant current charging voltage.
6. The method of claim 4, wherein controlling pulse characteristics
comprises applying an extended peak voltage for each voltage pulse
for a duration of time before the peak voltage is decreased.
7. The method of claim 4, wherein controlling pulse characteristics
comprises maintaining each valley between adjacent voltage pulses
at an equal valley voltage.
8. The method of claim 4, wherein controlling pulse characteristics
comprises gradually increasing, in succession, a valley voltage of
each valley between adjacent voltage pulses.
9. The method of claim 4, wherein controlling pulse characteristics
comprises maintaining each valley between adjacent voltage peaks at
a constant voltage for a duration of time.
10. The method of claim 4, wherein the pulse characteristics are
configured to optimize dissolution of lithium sulfide formed on the
sulfur-containing cathode of the battery.
11. An apparatus for charging a lithium-sulfur battery having at
least one unit cell comprising a lithium-containing anode and a
sulfur-containing cathode with an electrolyte layer there between,
the apparatus comprising: a memory; and a processor configured to
execute instructions stored in the memory to: apply voltage pulses
for an application period, the application period initiated when a
battery charge cycle is initiated, wherein the voltage pulses are
less than a constant current charging voltage; and initiate
constant current charging after the application period is
complete.
12. The apparatus of claim 11, wherein the processor is configured
to apply voltage pulses to create surface defects on lithium
sulfide particles.
13. The apparatus of claim 11, wherein the processor is configured
to control pulse characteristics of each voltage pulse while
applying the voltage pulses during the application period, the
pulse characteristics including one or more of a number of pulses,
a frequency of pulses, a pulse duration, a peak voltage, a pulse
shape, a valley duration and a valley valley voltage.
14. The apparatus of claim 13, wherein the processor is configured
to control pulse characteristics by gradually increasing, in
succession, the peak voltage of each of the voltage pulses, each
peak voltage being less than the constant current charging
voltage.
15. The apparatus of claim 13, wherein the processor is configured
to control pulse characteristics by applying the peak voltage for
each voltage pulse for a duration of time before the peak voltage
is decreased.
16. The apparatus of claim 13, wherein the processor is configured
to control pulse characteristics by applying an equal valley
voltage to each valley between adjacent voltage pulses.
17. The apparatus of claim 13, wherein the processor is configured
to control pulse characteristics by gradually increasing, in
succession, the valley valley voltage of each valley between
adjacent voltage pulses.
18. The apparatus of claim 13, wherein the processor is configured
to control pulse characteristics by maintaining each valley between
adjacent voltage pulses at a constant valley voltage for a duration
of time.
19. The apparatus of claim 13, wherein the processor is configured
to control the pulse characteristics to optimize dissolution of
lithium sulfide formed on the sulfur-containing cathode of the
battery.
20. A vehicle comprising the apparatus as claimed in claim 11.
Description
TECHNICAL FIELD
[0001] This disclosure relates to methods for improving the cell
life of a lithium sulfur battery, and in particular, methods for
improving dissolution of electronically resistive lithium sulfide
deposits that degrade cell performance.
BACKGROUND
[0002] The lithium-sulfur battery (Li--S battery) is a rechargeable
battery, notable for its high energy density. Li--S batteries may
be a successful alternative to lithium-ion cells because of their
higher energy density and reduced cost from the use of sulfur.
However, Li--S batteries do present some challenges that must be
addressed before the advantages of Li--S batteries can be fully
appreciated. For example, during discharge, a film-like insulating
layer of lithium sulfide can form on the cathode. During subsequent
charging, this insulating layer leads to high ohmic resistance and
voltage losses.
SUMMARY
[0003] Provided are methods and apparatus for charging a Li--S
battery. The Li--S battery has at least one unit cell comprising a
lithium-containing anode and a sulfur-containing cathode with an
electrolyte layer there between. One method provides controlled
application of voltage pulses at the beginning of the charging
process. An application period is initiated after a discharge cycle
of the Li--S battery is complete. During the application period,
voltage pulses are provided to the Li--S battery. The voltage
pulses are less than a constant current charging voltage. Constant
current charging is initiated after the application period has
elapsed.
[0004] An apparatus for charging a lithium-sulfur battery having at
least one unit cell comprising a lithium-containing anode and a
sulfur-containing cathode with an electrolyte layer there between
is also disclosed. The apparatus comprises a memory and a processor
configured to execute instructions stored in the memory to apply
voltage pulses for an application period, the application period
initiated when a battery charge cycle is initiated, wherein the
voltage pulses are less than a constant current charging voltage,
and initiate constant current charging after the application period
is complete.
[0005] These and other aspects of the present disclosure are
disclosed in the following detailed description of the embodiments,
the appended claims and the accompanying figures.
BRIEF DESCRIPTION OF THE DRAWINGS
[0006] The invention is best understood from the following detailed
description when read in conjunction with the accompanying
drawings. It is emphasized that, according to common practice, the
various features of the drawings are not to-scale. On the contrary,
the dimensions of the various features are arbitrarily expanded or
reduced for clarity. Included in the drawings are the following
figures:
[0007] FIG. 1 is a flow diagram of a method of charging a Li--S
battery as disclosed herein;
[0008] FIG. 2A is a diagram of current versus time for a Li--S
battery during discharging and charging using the methods disclosed
herein;
[0009] FIG. 2B is a diagram of voltage versus capacity for the
Li--S battery during discharging and charging using the methods
disclosed herein;
[0010] FIG. 3 is a schematic diagram illustrating pulse
characteristics;
[0011] FIGS. 4A and 4B are diagrams illustrating non-limiting
examples of pulses applied during the methods disclosed herein;
and
[0012] FIG. 5 is a schematic of an apparatus for charging a lithium
sulfide battery as disclosed herein.
DETAILED DESCRIPTION
[0013] Unlike in a lithium ion battery, lithium is not intercalated
inside another substance in the Li--S battery; rather, lithium
metal is the negative electrode. Sulfur is used as the positive
electrode active material. Because sulfur is well known as an
insulator, the sulfur is typically combined with a material having
good conductivity, such as carbon. A carbon coating can provide the
missing electronic conductivity. Carbon nanofibers can provide an
effective electron conduction path and structural integrity.
[0014] Chemical processes in the Li--S cell include lithium
dissolution from the anode surface (and incorporation into alkali
metal polysulfide salts) during discharge, and reverse lithium
plating to the anode while charging. Because the lithium ions are
not intercalated in the anode and cathodes as in the conventional
lithium ion cell, the Li--S cell allows for a much higher lithium
storage density. The lithium, during discharge, is transported
across the electrolyte from the anode to the cathode and reacts
with sulfur to undergo the following reaction, with a reverse
reaction occurring when the cell is charged:
S.sub.8.fwdarw.Li.sub.2S.sub.6.fwdarw.Li.sub.2S.sub.4.fwdarw.Li.sub.2S.s-
ub.3.fwdarw.Li.sub.2S.sub.2.fwdarw.Li.sub.2S
[0015] During discharge, lithium undergoes oxidation on the anode
and subsequently reacts with the sulfur on the cathode to form
lithium sulfide, Li.sub.2S. Lithium sulfide is an electronically
insulating and chemically insoluble species. Complete discharge of
the battery can lead to the formation of large agglomerated
particles of lithium sulfide or a film-like insulating layer of
lithium sulfide on the cathode. During a subsequent charge process,
the high electronic resistivity of the lithium sulfide species
leads to high ohmic resistance and voltage losses, resulting in
poor coulombic efficiency, defined as follows:
.eta. c = Q out Q i n ##EQU00001##
[0016] where .eta..sub.c is the coulombic efficiency, Q.sub.out is
the amount of charge that exits the battery during the discharge
cycle and Q.sub.in is the amount of charge that enters the battery
during the charging cycle.
[0017] As the insulating film continues to accumulate irreversibly
over the cycling process, less lithium and sulfur are available as
active species, leading to exponentially decreasing capacity.
[0018] The device and methods herein address these deficiencies in
the Li--S battery by disrupting the film-like insulating layer on
the cathode, thereby improving the Li--S battery's coulombic
efficiency, improving the battery's charge efficiency, enhancing
the battery's rate capability, decreasing charge cycle duration and
reclaiming active sulfur particles.
[0019] FIG. 1 is a flow diagram of a method of charging a Li--S
battery as taught herein. The Li--S battery has at least one unit
cell comprising a lithium-containing anode and a sulfur-containing
cathode with an electrolyte layer there between. The method
provides controlled application of voltage pulses at the beginning
of the charging process. In step S10, an application period is
initiated when a charge cycle of the Li--S battery is initiated. In
step S20, during the application period, voltage pulses are
provided to the Li--S battery. The voltage pulses are less than a
constant current charging voltage. In step S30, constant current
charging is initiated after the application period has elapsed.
[0020] The charge cycle is typically initiated directly after a
discharge cycle is complete, which is typically when the battery is
about 20% state-of-charge. However, the charge cycle may be
initiated at any time after some discharge has occurred. Initiation
of the charge cycle can occur when, for example, the vehicle is
connected to a charger. It should be noted that the application
period does not need to be initiated every time a charge cycle is
initiated. For example, if the battery has only been discharged to
50%, lithium sulfide may have not yet started to agglomerate or
form the film-like insulating layer. The application period is not
yet necessary. Therefore, the application period may only be
applied when a charge cycle is started and the battery is at 80% of
discharge or more, as a non-limiting example.
[0021] FIGS. 2A and 2B illustrate the application of voltage during
the charge/discharge cycles and the battery capacity over time,
respectively. As seen in FIGS. 2A and 2B, as the battery
discharges, the battery capacity decreases and Li and S form
Li.sub.2S. Line D/C represents the completion of the discharge
cycle and the initiation of the charge cycle. The broken line A in
both FIGS. 2A and 2B represent the constant charge and the jump in
battery capacity that occurs during conventional charging. As shown
in FIG. 2A, conventionally charging at a constant current occurs
until the battery has reached its maximum charge capacity. As shown
in FIG. 2B, high ohmic voltage loss X occurs upon start of the
constant current charging due to the electronically insulating
Li.sub.2S film on the cathode. The voltage provided in FIG. 2B is
provided by way of illustration and is not meant to be
limiting.
[0022] As illustrated in FIGS. 2A and 2B, the application period T
begins at line D/C, when discharge is complete. Rather than
initiating charging at the constant current, voltage pulses V are
applied during the application period T. When the application
period T is complete, constant current charging C is initiated.
[0023] The application period T can be predetermined based on prior
evaluations of Li--S batteries. The application period T can be
constant throughout the battery life or can be programmed to change
based on the number of discharge and charge cycles the battery has
experienced. For example, as the number of cycles experienced by
the battery increases, the application period T can increase. The
Li--S battery system can include one or more sensors that provide
battery information to a controller that can adjust the application
period T based on the output of the sensor or sensors. As a
non-limiting example, the coulombic efficiency of the battery can
be calculated by the controller and the application period T
extended as the efficiency drops.
[0024] The voltage pulses V applied during the application period T
create surface defects on the lithium sulfide particles, minimizing
the activation energy barrier for lithium sulfide oxidation, and
thereby facilitating the dissolution and the reactivity of the
lithium sulfide particles. As the defects are created in the
lithium sulfide, the lithium sulfide particles dissolve, thereby
removing the insulating layer as additional lithium sulfide
particles dissolve. The dissolved lithium and sulfur become
available as active particles again.
[0025] By applying a voltage pulse (less than voltage at constant
charging current) the lithium sulfide layer is not decomposed at
once, but rather is decomposed in multiple steps. Initial voltage
pulses will start by making small defects (i.e. point, line or even
plane defects) on the surface of the lithium sulfide particles. The
non-perfect lithium sulfide formed during the initial pulses is
more reactive and less insulating, thereby allowing its reduction
during the charging process at lower voltages than the one at
constant current.
[0026] It should be noted that the anode chemistry is unchanged
during the application period. The voltage pulses target the
lithium sulfide forming a coating on the cathode. Characteristics
of the applied voltage peaks can be manipulated to optimize the
dissolution of the lithium sulfide particles while minimizing any
negative effects on the battery cells. The pulse characteristics
include a number of pulses, a frequency of pulses, a pulse
duration, a peak voltage, a pulse shape, a peak duration, a valley
duration and a valley voltage. One or more pulse characteristics
can be manipulated to obtain the desired results.
[0027] FIG. 3 illustrates the different pulse characteristics. As
shown in FIG. 3, two pulses 1, 2 are illustrated. The peak voltage
for each pulse is represented by "a", pulse duration is represented
by "b", valley duration is represented by "c", valley voltage is
represented by "d", peak duration is represented by "e" and change
in peak is represented by "f".
[0028] FIGS. 4A and 4B are illustrations of different pulse
characteristics that can be applied during the application period T
and are provided as non-limiting examples only. In FIG. 4A, the
peak voltage a, a', a'' gradually increases, in succession, for
each of the three pulses V, V', V'' applied during the application
period T. Each peak voltage a, a', a'' is less than the constant
current charging voltage C. The pulse characteristics in FIG. 4A
are also controlled to apply an extended peak voltage for each
voltage pulse V, V', V'' for a peak duration e of time before the
peak voltage a, a', a'' is decreased. Although both the peak
duration "e" and the pulse duration b are shown as the same for
each voltage pulse V, V', V'', one or both of the peak duration "e"
and the pulse duration b can be different for one or all of the
voltage pulses. FIG. 4A also illustrates controlling pulse
characteristics so that a valley voltage d, d' of each valley
between adjacent voltage pulses is gradually increased in
succession.
[0029] In FIG. 4B, the peak voltage "a" is the same for each pulse
V, V'' applied during the application period T. The pulse
characteristics in FIG. 4B are also controlled to maintain each
valley between adjacent voltage pulses V, V' at an equal valley
voltage "d". Each valley between adjacent voltage peaks V, V' is
maintained at "a" constant voltage for a valley duration "c" of
time. As in FIG. 4A, each peak voltage "a" is less than the
constant current charging voltage C. The valley voltage "d" in each
of FIGS. 4A and 4B is illustrated as being greater than the
discharged voltage D of the battery, illustrated in FIG. 3 as 1.7V
by means of example.
[0030] Also disclosed herein is an apparatus for charging a
lithium-sulfur battery having at least one unit cell comprising a
lithium-containing anode and a sulfur-containing cathode with an
electrolyte layer there between. The apparatus 100 is illustrated
in FIG. 5 as a computing device having a memory and a processor
configured to execute instructions stored in the memory. The
apparatus 100 is illustrated as being on board the vehicle 110 and
may be included in a telematics unit of the vehicle 110 as a
non-limiting example. However, it is understood that the apparatus
100 may be located remote from the vehicle 110 and receiving and
transmitting information wirelessly with the vehicle 110, through,
for example, the telematics unit.
[0031] The apparatus 100 performs the methods described herein by
communicating with the battery charging system 112 to apply voltage
pulses to the battery 114 for an application period, the
application period initiated when a battery charge cycle is
initiated. The battery charging system 112 is shown on-board
vehicle 110 and can be an on-board energy source, such as another
battery or a capacitor. The battery or capacitor can be charged,
for example, by an on-board regenerative braking system or an
off-board charger. The battery charging system 112 can also be an
off-board charger to which the vehicle battery 114 is connected
when charging is desired or required. The apparatus 100
communicates with the battery charging system 112 to maintain
voltage pulses less than a constant current charging voltage and to
control the pulse characteristics of the voltage pulses as
described above. The apparatus 100 communicates with the battery
charging system 112 to initiate constant current charging after the
application period is complete. It is understood that the apparatus
100 can be a part of the battery charging system 112 if desired, or
can be a separate unit as illustrated.
[0032] Implementations of computing devices to carry out the
processes (and the algorithms, methods, instructions, etc., stored
thereon and/or executed thereby as described herein) may be
realized in hardware, software, or any combination thereof. The
hardware can include, for example, computers, IP cores, ASICs,
PLAs, optical processors, PLCs, microcode, microcontrollers,
servers, microprocessors, digital signal processors or any other
suitable circuit. In the claims, the term "processor" should be
understood as encompassing any of the foregoing hardware or other
like components to be developed, either singly or in
combination.
[0033] In one example, a computing device may be implemented using
a general purpose computer or general purpose processor with a
computer program that, when executed, carries out any of the
respective methods, algorithms and/or instructions described
herein. In addition or alternatively, for example, a special
purpose computer/processor can be utilized which can contain other
hardware for carrying out any of the methods, algorithms, or
instructions described herein. Further, some or all of the
teachings herein may take the form of a computer program product
accessible from, for example, a tangible (i.e., non-transitory)
computer-usable or computer-readable medium. A computer-usable or
computer-readable medium is any device that can, for example,
tangibly contain, store, communicate, or transport the program for
use by or in connection with any processor. The medium may be an
electronic, magnetic, optical, electromagnetic or semiconductor
device, for example.
[0034] As described herein, the processes include a series of
steps. Unless otherwise indicated, the steps described may be
processed in different orders, including in parallel. Moreover,
steps other than those described may be included in certain
implementations, or described steps may be omitted or combined, and
not depart from the teachings herein.
[0035] All combinations of the embodiments are specifically
embraced by the present invention and are disclosed herein just as
if each and every combination was individually and explicitly
disclosed, to the extent that such combinations embrace operable
processes and/or devices/systems. In addition, all sub-combinations
listed in the embodiments describing such variables are also
specifically embraced by the present device and methods and are
disclosed herein just as if each and every such sub-combination was
individually and explicitly disclosed herein.
[0036] While the invention has been described in connection with
what is presently considered to be the most practical and preferred
embodiment, it is to be understood that the invention is not to be
limited to the disclosed embodiments but, on the contrary, is
intended to cover various modifications and equivalent arrangements
included within the spirit and scope of the appended claims, which
scope is to be accorded the broadest interpretation so as to
encompass all such modifications and equivalent structures as is
permitted under the law.
* * * * *